Alkylglycosides have been known for a long time and are used, among other things, as detergents because of their surfactant properties. The alkylglycosides whose alkyl residue contains a carbon number of at least 8 are especially interesting in this regard.
Since the alkylglycosides can be manufactured completely from renewable raw materials--they are obtained primarily from fatty alcohols, which can be obtained from natural fats, and saccharides--there has been no lack of effort to improve the processes used in industry. Thus, numerous catalyst systems have been developed to influence the primarily acid-catalyzed reaction advantageously. There has also been no lack of effort to develop processes that can be performed continuously.
Thus, in particular, there are many methods in which C.sub.1 -C.sub.4 glycosides are produced continuously and then reacetalized in a second step with fatty alcohols to produce the actual washing-active product. These processes are generally referred to as two-stage processes.
U.S. Pat. No. 4,223,129 describes a continuous process in which polysaccharides and corresponding monoalcohols are reacted in a device in which the main reaction takes place mainly in a coiled tube. According to this U.S. patent, the process is also intended to be applicable to the reaction of alkyl alcohols with up to 18 carbon atoms. It has developed, however, that the reaction is difficult to control, the yields are not optimal, and moreover the water created in the reaction can only be drawn off at a later point in time, so that this cannot be termed a completely continuous process that operates satisfactorily.
European Patent Application No. 0 378 710 describes a process in which a heterogeneous acid catalyst is used. When the reaction mixture is no longer in contact with the catalyst, alkylglycoside is crystallized out and separated by adding an apolar solvent. The mother liquor is recycled back to the process after the solvent is separated out.
EP-A2-0 448 794 describes a process for manufacturing alkylglycosides in which alcohols are reacted with saccharides in a single stage. The process can also be operated continuously. It is necessary to carry out the reaction in the presence of a nonpolar solvent, an emulsifier, and relatively large quantities of an acid catalyst.
Although a number of processes for manufacturing alkylglycosides are already known, there is a great need for an improved single-stage fully continuous process, with the term "single-stage processing" meaning one in which the corresponding long-chain alkyl alcohol and saccharide are reacted directly with one another.